The present invention relates to a new and improved method of extracting or recovering furfural, acetic acid and formic acid and other organic compounds from acidic hydrolysates of plants or vegetable matter.
Furfural can be obtained by the hydrolysis of pentosan-containing plants or their waste products. The plant or vegetable material is treated in the presence of acidic conditions at temperatures below 200.degree. C. in a hydrolysis apparatus (cooker). Thereafter the furfural is obtained by treatment with steam (approximately 20 tons steam per ton furfural). These techniques are extremely energy consuming and, thus, usually in the furfural installations or plants, the plant material which has been cooked out is combusted following the hydrolysis and the heat of combustion is beneficially employed for generating the required steam.
In cellulose plants the recovery of cellulose is of primary importance and, generally, the pentosans together with the lignin and other hydrolysis products in the spent liquor are concentrated and combusted. In particular, during the hydrolysis or disintegration of deciduous wood and young plants, typically year old plants, there are combusted large quantities of pentosans (approximately 20% of the raw material). Therefore, numerous experiments have already been carried out for the purpose of extracting furfural from spent or waste sulfite liquors by converting the pentosans, and there has been performed a pressurised heating of the spent sulfite liquors at 150.degree. C. to 180.degree. C. for a number of hours with subsequent distillation of the spent sulfite liquor. Due to the long heating of the spent sulfite liquor a large quantity of the extracted or recovered furfural is again decomposed. Furthermore, the distillation of the furfural from the spent sulfite liquor requires large quantities of steam, and specifically, in order to extract 1 ton of furfural there are required 50 to 60 tons of steam.
In Austrian Pat. No. 356,509 there is disclosed a method wherein the substance contents of spent sulfite liquors and their vapour condensates can be economically recovered by extraction with liquid ion exchangers. The drawback of this prior art method resides in the fact that while there can be recovered completely the acetic acid which is formed during the hydrolysis or solubilisation, nonetheless the pentosans are still combusted in the form of xylose or wood sugar.